Lots of true hip hop is based around the idea of a concept album. Some artists just create a character for themselves and stick to that one persona. This is how gangster rap began, similar to creating a character in a movie. Kool Keith made the concept album popular as he released albums related so several characters he created. His character Dr. Doom is an evil villain that is on an album. The next album is about the crazed Dr. Octagon who kills Dr. Doom at the beginning of the album. Keith was one of the first artists to create different identities for his albums and to wear costumes both on stage and in his videos. His style of rapping is very abstract and strange. These concepts have been used today by a variety of artists (watch an Eminem video).
In hip hop there are a large amount of concept albums. Handsome Boy Modeling School was originally a sketch on the Chris Elliot Show, and was turned into two albums by Prince Paul and Dan the Automator. Before working on these projects, Prince Paul created the first hip-hopera; a story about a boy growing up in the ghetto with aspirations to rap but finding drugs, jail and eventually his death blocking his dreams. One of my favorite concept albums is Deltron 3030, collaboration between Del the Funkee Homosapien, Kid Koala, and Dan the Automator. In this album each artist takes on a futuristic personal and raps about the build up of technology and the destruction of the planet. This style of writing is very creative and brings a fresh perspective to the hip hop style.